This invention relates generally to gas turbine engine rotor assemblies and more particularly to a blade retention system for a gas turbine engine rotor assembly.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. In a turbofan engine, which typically includes a fan placed at the front of the core engine, a high pressure turbine powers the compressor of the core engine. A low pressure turbine is disposed downstream from the high pressure turbine for powering the fan. Each turbine stage commonly includes a stationary turbine nozzle followed in turn by a turbine rotor.
A turbine rotor comprises a row of rotor blades mounted to the perimeter of a rotor disk that rotates about the centerline axis of the engine. Each rotor blade typically includes a shank portion having a dovetail for mounting the blade to the rotor disk and an airfoil that extracts useful work from the hot gases exiting the combustor. A blade platform, formed at the junction of the airfoil and the shank portion, defines the radially inner boundary for the hot gas stream. The turbine nozzles are usually segmented around the circumference thereof to accommodate thermal expansion. Each nozzle segment has one or more nozzle vanes disposed between inner and outer bands for channeling the hot gas stream into the turbine rotor.
To improve turbine engine performance, flowpath temperatures and blade tip speeds are increased. These conditions increase centrifugal loads and metal temperatures, requiring robust turbine blade and blade retainer designs. Rotor cavities are shielded from flowpath temperatures by overlap seals, formed by a combination of sealing flanges, often referred to as “angel wings”, which are mounted on the blades, blade retainers, or stator. This configuration isolates flowpath gas ingestion to one or more buffer cavities. Hotter flowpath temperatures require improved sealing of turbine rotor purge cavities. However, overlap seals become more difficult to design as centrifugal loads and temperatures increase. Prior art sealing configurations typically use either a single or double overlap angel wing arrangement, using 360 degree or segmented sealing components for the rotor and stator.
When buffer cavity temperatures exceed the temperature capabilities of forged superalloy materials, cast segmented arcuate retainers are often used to replace the outer most portion of blade retainers. These segmented retainers or “chicklets” have typically been constrained radially with dovetails, similar to the manner in which turbine blades are retained in the rotor. Dovetailed chicklets are challenging to design, especially for single tang blades, and relatively costly to manufacture. Flowpath gas leakage also occurs through the gaps between adjacent retainers.
Accordingly, there is a need for an improved blade retainer system.